Abstract
Development of a viral vector that can infect hair cells of the cochlea without producing viral-associated ototoxic effects is crucial for utilizing gene replacement therapy as a treatment for certain forms of hereditary deafness. In the present study, cochlear function was monitored using distortion-product otoacoustic emissions (DPOAEs) in guinea pigs that received infusions of either (E1-, E3-) adenovirus, or adeno-associated virus (AAV), directly into the scala tympani. Replication-deficient (E1-, E3-) adenovirus-directed gene transfer, using the cytomegalovirus (CMV) promoter, drove transgene expression to inner hair cells and pillar cells of the cochlea. AAV transduction was tested with several promoters, such as platelet-derived growth factor (PDGF), neuron-specific enolase(NSE), and elongation factor 1α (EF-1α) promoters; which drove transgene expression to cochlear blood vessels, nerve fibers, and certain spiral limbus cells, respectively. AAV transgene expression was visualized by green fluorescent protein immunostaining. Immunocytochemistry to heparan sulfate confirmed the absence of proteoglycans in guinea pig hair cells, indicating that the receptor for AAV was not present on these cells. However, the heparan sulfate proteoglycan expression pattern mimicked the AAV transduction pattern. An overall finding was that cochlear function was not altered throughout the infection period using AAV titers as high as 5 × 108 IP/infused cochlea. In contrast, cochlear function was severely compromised by 8 days postinfection with adenoviral titers of 5 × 108 PFU/infused cochlea, and outer hair cells were eliminated. Thus, cochlear hair cells are amenable to in vivo gene transfer using a replication-deficient (E1-, E3-) adenovirus. However, replication-defective or gutted adenovirus vectors must be employed to overcome the ototoxic effects of (E1-, E3-) adenovirus vectors.
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